硫碘循环制氢中电化学Bunsen反应特性研究
发布时间：2018-09-12 12:50
【摘要】：作为清洁、高效、安全和可持续的替代能源,氢能日渐受到人类青睐,未来有望建立集成制氢、储氢、输运及转化利用等多环节的氢能系统,实现全球化石能源经济向氢能经济的转型。氢气制备是构建氢能系统的首要工作,而利用资源丰富且无污染的水制取氢气是公认的最佳选择。其中,热化学循环水分解制氢方法由于具备诸多优点而受到重视,尤其是硫碘循环被认为是最有前景的方法之一。热化学硫碘循环水分解制氢中第一步Bunsen反应(SO2+12+2H2O→ H2SO4+2HI)的实现方法及进行程度等影响后续HI和H2SO4分解反应,制约着整个硫碘循环系统。传统Bunsen反应延续的是美国GA公司提出的在过量碘和水的条件下进行反应,生成HI和H2SO4自发分层。为了减少甚至避免过量碘和水的加入,电化学Bunsen反应方法应运而生,有望实现硫碘循环系统的简化。鉴于实际硫碘循环系统中有HI返回Bunsen反应,针对初始HI存在下的四元多相Bunsen反应动力学和热力学平衡进行研究。提高初始HI浓度或者温度加快了反应动力学速率,液。液分层提前出现,且缩短了达到热力学平衡的时间。但HI量过高不利于两相分离,故HI/H2O摩尔比须控制在0～1/18的合理范围内。提高初始HI量增加了H2SO4相杂质,但提高温度改善了液-液相平衡分离特性。加入初始HI使HIx相中HI浓度达到了超恒沸,有利于减少后续HI浓缩步骤,实现硫碘循环系统的优化。提高初始HI量或温度造成SO2平衡转化率略有降低。综合考虑,较高温度345～358K、HI/H2O摩尔比0～1/36是比较理想的工况范围。围绕电化学Bunsen反应开展了基础实验研究,探讨了两极酸溶液浓缩和电池电压的变化规律。随着电解进行,阳极H2SO4和阴极HI的浓度均呈上升趋势,阴极12浓度降低,而电压整体呈现上升趋势。提高电流密度增加了单位时间内得失电子数,生成H2SO4和HI量增加且电压增大,但电压超过3V会造成阳极侧石墨电极的腐蚀。提高温度加快了电极反应速率。增加12/HI摩尔比既可降低过电势也可增大溶液欧姆电阻。大部分工况条件下电流效率大于90%,甚至接近100%,表明了该电池能量转化性能较好。增加电流密度增大了能耗,而提高温度或H28O4浓度则相反；改变HI浓度或12/HI摩尔比时,则出现峰值能耗。以代表性的Nafion 117和115膜为研究对象,探讨了质子交换膜在电池中的特性。膜的质子传递数t+基本上大于0.9,甚至接近1,除了在高温下,Nafion 115膜的质子传递能力显著下降；水的渗透系数β依据工况条件变化不一。膜的传输特性与酸浓缩效果密切相关,高t+和低β值易获得高浓度HI；相反,可生成高浓度H2SO4。分析膜两侧交叉污染时,发现阳极HI比阴极H2S04的浓度高2-10倍。提高电流密度、温度或初始I-/HI摩尔比,HI和1-12S04的摩尔通量均增加。提高H2SO4浓度促进H2S04传递而抑制HI渗透,提高HI浓度时情况相反。膜的微观表征表明电化学反应后的膜出现褶皱且有固体颗粒沉积,造成了BET表面积增大和平均孔径减小。经活化后,膜的性能得到恢复,有利于延长其寿命。对电化学Bunsen反应的平衡电势进行了实验和理论研究,首先基于电化学原理推导出平衡电势的理论模型,其次通过实验探讨了各参数对平衡电势的影响。提高S02或12浓度会降低平衡电势,而提高H2SO4或HI浓度则相反；温度升高,平衡电势会降低。通过对实验数据拟合分析验证了该模型的准确性,并确定了代表电解质非理想特性和膜内浓度分布的参数M和Z均与溶液浓度无关,Z基本不随温度变化,但M与温度存在指数关系,温度越高,M值越低。最后,提出了平衡电势经验公式,可以很好地重现实验数据,实现了电池平衡电势的预测。基于电化学工作站原理研究了电化学Bunsen反应的电极反应机理及动力学特性,利用循环伏安法测量两极反应,判断出阳极SO2氧化和阴极12还原均不可逆：依据峰值电流定性分析了扩散传质速率。测量两极反应的电化学阻抗谱,并对Nyquist图作等效电路拟合。阴极反应等效电路为一个溶液欧姆电阻串联着一对并联的电荷传递电阻和常相位角元件；阳极反应等效电路由电荷传递电阻和常相位角元件并联组成。计算并评估了交换电流密度(j0)和标准反应速率常数(k0)两个重要动力学参数,当阴极HI浓度为8mol/kgH2o、I2/HI摩尔比为0.5,阳极H2SO4浓度为13mol/kgH2O时可以获得较高的电极反应动力学速率。对基于电化学Bunsen反应的硫碘循环系统进行了流程设计和模拟,计算了产氢量为1mol/s时的系统质量平衡和能量平衡。考虑内部换热、废热回收发电,计算出系统热效率达48.98%。相比于使用传统Bunsen反应的硫碘循环系统,使用电化学Bunsen反应的硫碘循环系统极大地简化了流程,降低了能耗,从而提高了热效率。通过改进优化,未来有望进一步提高系统热效率及经济性。
[Abstract]:As a clean, efficient, safe and sustainable alternative energy source, hydrogen energy is becoming more and more popular. It is expected to build an integrated hydrogen production, hydrogen storage, transportation and conversion system in the future, and realize the transition from global fossil energy economy to hydrogen economy. Hydrogen production from non-polluted water is recognized as the best choice. Thermochemical cycling water decomposition is one of the most promising methods because of its many advantages, especially the sulfur-iodine cycle. The traditional Bunsen reaction continues the spontaneous stratification of HI and H2SO4 by the reaction of excessive iodine and water proposed by GA Company in the United States. In order to reduce or even avoid the addition of excess iodine and water, the electrochemical Bunsen reaction method is applied. In view of the fact that HI returns to Bunsen reaction in the actual sulfur-iodine cycle system, the kinetics and thermodynamic equilibrium of the quaternary-multiphase Bunsen reaction in the presence of initial HI are studied. However, the high HI content is not conducive to the separation of the two phases, so the HI/H2O molar ratio should be controlled within a reasonable range of 0-1/18. Increasing the initial HI content increases the impurities of H2SO4 phase, but improves the liquid-liquid equilibrium separation characteristics by increasing the temperature. Adding the initial HI makes the HI concentration in the HIx phase reach super-boiling, which is conducive to reducing the subsequent HI concentration. Increasing the initial HI or temperature results in a slight decrease in the equilibrium conversion of SO2. Considering the high temperature of 345-358K, the HI/H2O molar ratio of 0-1/36 is an ideal operating range. The basic experimental study was carried out around the electrochemical Bunsen reaction, and the concentration of bipolar acid solution and the voltage of the battery were discussed. With the electrolysis proceeding, the concentration of H2SO4 on the anode and HI on the cathode increased, the concentration of 12 on the cathode decreased, while the voltage on the cathode increased as a whole. Increasing the 12/HI molar ratio can reduce the overpotential and increase the ohmic resistance of the solution. The current efficiency is more than 90% or even close to 100% under most operating conditions, indicating that the energy conversion performance of the battery is good. Increasing the current density increases the energy consumption, while changing the HI concentration or the high temperature or H28O4 concentration is opposite. The characteristics of proton exchange membranes in batteries were studied. The proton transfer number T + of the membranes was more than 0.9 or even close to 1. Except at high temperature, the proton transfer capacity of Nafion 115 membrane decreased significantly; the water permeability coefficient beta depended on the operating conditions. The transport characteristics of the membrane are closely related to the concentration of acid. On the contrary, high concentration of H2SO4 can be obtained easily with high T + and low beta values. When analyzing the cross contamination on both sides of the membrane, it is found that the concentration of anodic HI is 2-10 times higher than that of cathode H2S04. Increasing the concentration of H2SO4 promotes the transmission of H2S04 and inhibits the infiltration of HI, whereas increasing the concentration of HI is contrary. The microscopic characterization of the membrane shows that the membrane after electrochemical reaction has folds and solid particles deposition, resulting in the increase of BET surface area and the decrease of average pore size. The equilibrium potential of en reaction was studied experimentally and theoretically. Firstly, the theoretical model of equilibrium potential was deduced based on electrochemical principle. Secondly, the effect of various parameters on equilibrium potential was discussed experimentally. The accuracy of the model is verified by fitting and analyzing the experimental data. The parameters M and Z, which represent the non-ideal characteristics of electrolyte and the concentration distribution in the membrane, are independent of the solution concentration. Z does not change with the temperature. However, there is an exponential relationship between M and temperature. The higher the temperature, the lower the M value. Based on the principle of electrochemical workstation, the electrode reaction mechanism and kinetic characteristics of electrochemical Bunsen reaction were studied. The cyclic voltammetry was used to measure the bipolar reaction and the irreversibility of anodic SO2 oxidation and cathode 12 reduction was judged. The cathode reaction equivalent circuit consists of a solution ohmic resistance in series with a pair of parallel charge transfer resistors and constant phase angle elements; the anode reaction equivalent circuit consists of a charge transfer resistor and a constant phase angle element in parallel. Exchange current density (j0) and standard reaction rate constant (k0) are two important kinetic parameters. When the cathode HI concentration is 8mol/kg H2o, the I2/HI molar ratio is 0.5, and the anode H2SO4 concentration is 13mol/kg H2O, a higher electrode reaction kinetic rate can be obtained. The mass balance and energy balance of the system with hydrogen yield of 1 mol/s are calculated. Considering internal heat transfer and waste heat recovery, the thermal efficiency of the system is calculated to be 48.98%. Compared with the traditional Bunsen reaction sulfur-iodine cycle system, the electrochemical Bunsen reaction sulfur-iodine cycle system greatly simplifies the process, reduces the energy consumption and thus improves the energy consumption. By improving and optimizing, it is expected to further improve the thermal efficiency and economy of the system.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TQ116.2
本文编号：2239054
[Abstract]:As a clean, efficient, safe and sustainable alternative energy source, hydrogen energy is becoming more and more popular. It is expected to build an integrated hydrogen production, hydrogen storage, transportation and conversion system in the future, and realize the transition from global fossil energy economy to hydrogen economy. Hydrogen production from non-polluted water is recognized as the best choice. Thermochemical cycling water decomposition is one of the most promising methods because of its many advantages, especially the sulfur-iodine cycle. The traditional Bunsen reaction continues the spontaneous stratification of HI and H2SO4 by the reaction of excessive iodine and water proposed by GA Company in the United States. In order to reduce or even avoid the addition of excess iodine and water, the electrochemical Bunsen reaction method is applied. In view of the fact that HI returns to Bunsen reaction in the actual sulfur-iodine cycle system, the kinetics and thermodynamic equilibrium of the quaternary-multiphase Bunsen reaction in the presence of initial HI are studied. However, the high HI content is not conducive to the separation of the two phases, so the HI/H2O molar ratio should be controlled within a reasonable range of 0-1/18. Increasing the initial HI content increases the impurities of H2SO4 phase, but improves the liquid-liquid equilibrium separation characteristics by increasing the temperature. Adding the initial HI makes the HI concentration in the HIx phase reach super-boiling, which is conducive to reducing the subsequent HI concentration. Increasing the initial HI or temperature results in a slight decrease in the equilibrium conversion of SO2. Considering the high temperature of 345-358K, the HI/H2O molar ratio of 0-1/36 is an ideal operating range. The basic experimental study was carried out around the electrochemical Bunsen reaction, and the concentration of bipolar acid solution and the voltage of the battery were discussed. With the electrolysis proceeding, the concentration of H2SO4 on the anode and HI on the cathode increased, the concentration of 12 on the cathode decreased, while the voltage on the cathode increased as a whole. Increasing the 12/HI molar ratio can reduce the overpotential and increase the ohmic resistance of the solution. The current efficiency is more than 90% or even close to 100% under most operating conditions, indicating that the energy conversion performance of the battery is good. Increasing the current density increases the energy consumption, while changing the HI concentration or the high temperature or H28O4 concentration is opposite. The characteristics of proton exchange membranes in batteries were studied. The proton transfer number T + of the membranes was more than 0.9 or even close to 1. Except at high temperature, the proton transfer capacity of Nafion 115 membrane decreased significantly; the water permeability coefficient beta depended on the operating conditions. The transport characteristics of the membrane are closely related to the concentration of acid. On the contrary, high concentration of H2SO4 can be obtained easily with high T + and low beta values. When analyzing the cross contamination on both sides of the membrane, it is found that the concentration of anodic HI is 2-10 times higher than that of cathode H2S04. Increasing the concentration of H2SO4 promotes the transmission of H2S04 and inhibits the infiltration of HI, whereas increasing the concentration of HI is contrary. The microscopic characterization of the membrane shows that the membrane after electrochemical reaction has folds and solid particles deposition, resulting in the increase of BET surface area and the decrease of average pore size. The equilibrium potential of en reaction was studied experimentally and theoretically. Firstly, the theoretical model of equilibrium potential was deduced based on electrochemical principle. Secondly, the effect of various parameters on equilibrium potential was discussed experimentally. The accuracy of the model is verified by fitting and analyzing the experimental data. The parameters M and Z, which represent the non-ideal characteristics of electrolyte and the concentration distribution in the membrane, are independent of the solution concentration. Z does not change with the temperature. However, there is an exponential relationship between M and temperature. The higher the temperature, the lower the M value. Based on the principle of electrochemical workstation, the electrode reaction mechanism and kinetic characteristics of electrochemical Bunsen reaction were studied. The cyclic voltammetry was used to measure the bipolar reaction and the irreversibility of anodic SO2 oxidation and cathode 12 reduction was judged. The cathode reaction equivalent circuit consists of a solution ohmic resistance in series with a pair of parallel charge transfer resistors and constant phase angle elements; the anode reaction equivalent circuit consists of a charge transfer resistor and a constant phase angle element in parallel. Exchange current density (j0) and standard reaction rate constant (k0) are two important kinetic parameters. When the cathode HI concentration is 8mol/kg H2o, the I2/HI molar ratio is 0.5, and the anode H2SO4 concentration is 13mol/kg H2O, a higher electrode reaction kinetic rate can be obtained. The mass balance and energy balance of the system with hydrogen yield of 1 mol/s are calculated. Considering internal heat transfer and waste heat recovery, the thermal efficiency of the system is calculated to be 48.98%. Compared with the traditional Bunsen reaction sulfur-iodine cycle system, the electrochemical Bunsen reaction sulfur-iodine cycle system greatly simplifies the process, reduces the energy consumption and thus improves the energy consumption. By improving and optimizing, it is expected to further improve the thermal efficiency and economy of the system.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TQ116.2
【相似文献】
相关期刊论文 前1条
1 吴小兰;王倩;高云芳;;烟气脱硫Bunsen反应器设计[J];浙江化工;2012年09期
相关博士学位论文 前1条
1 应芝;硫碘循环制氢中电化学Bunsen反应特性研究[D];浙江大学;2015年
相关硕士学位论文 前1条
1 刘广义;热化学硫碘循环制氢中Bunsen反应与碘化氢分解的模拟与实验研究[D];浙江大学;2006年
，本文编号：2239054
本文链接：https://www.wllwen.com/kejilunwen/huagong/2239054.html
